The joining together of component parts or elements is a major problem in both the assembly and packaging of electrical and electronic devices and equipment. Traditionally, glass parts have been sealed to each other, or to ceramic or metal parts, by a direct process wherein the sealing surface of a glass part is thermally softened to the point where it will wet the sealing surface of another part. The sealing surfaces are then brought together with suitable working to effect an appropriate seal. This process is eminently successful where distortion of the glass member is tolerable, and where there are no thermally sensitive parts involved in the sealed product.
Where the distortion inherent in direct sealing cannot be tolerated, it is common practice to use an intermediate sealing material. In the event a hermetic and/or thermally resistant seal is required, a soft sealing glass, commonly referred to as a solder glass, may be used. The solder glass used in making such a seal must be one having a softening temperature well below the deformation temperature of any surface to which it is applied so that the glass can flow and wet the sealing surface at a temperature below that at which such surface becomes deformed. Also, the well-known rules of matching thermal expansion coefficients must be observed.